Method of making insulated cores



June 22, 1948. M. w. RIDER ETAL r 2,443,663

METHOD OF MAKING INSULATED CORES I Filed Feb. 1, 1945 Fly!) 4 4 M /2 24 2s 0 1113: 4 22 z 7 T flz'r wnuzssas: INVENTORS fiaryan M X er and X I We 4 and!- lamination insulation for several reasons. organic material available to the art will with- Potented June 22,

METHOD OF MAKING INSULATED CORES Morgan W. Rider, McKeespoi-t, and Weldon H.

Brandt, Wilkinsburg, Pa, assignors to West-. inghouse Electric Corporation, East Pittsburgh; Pa., a corporation of Pennsylvania Application February 1, 1945, Serial No. 515,647

5 Claims. I (Cl. 154-25) This invention relates to a process for applying flake insulation to electrical members.

- In the process of building electrical members, particularly magnetic cores composed of lamina.- tions of sheet magnetic material, it is necessary that the layers forming the laminations of the core be insulated from one another in order to reduce the electrical losses'during operation. The magnetic material is frequently bent or mechanically deformed when being formed into the core and becomes strained due to such deformation. Strains introduced into magnetic material increases electrical losses and accordingly the assembled core is annealed at an elevated temperature in order to eliminate the mechanical strains. Wound cores consisting of a plurality of turns of a magnetic material in particular must be strain annealed in order to secure a suitable low loss core.

One of the critical problems involving the manufacture of cores has been the introduction as interlamination insulation a material which will permit winding or otherwise building up.

magnetic cores capable of withstanding the strain anneal temperatures applied to the completed cores. The space factor should be low in order to permit satisfactory commercial manufacture.

Organic materials are not desirable as interstand the elevated annealing temperatures without evaporating, decomposing, or otherwise deteriorating to produce a carbonaceous conducting fmass. Further, at elevated temperatures, organic torily insulated core by attempting to introduce interlamination insulation after the core is built.

The object of this invention is to provide for applying inorganic insulation, capable of withstanding elevated temperatures, to sheet material. A further object of the invention is to provide for applying a substantiallysingle thickness of mica flakes to sheet magnetic material.

A still further object of the invention is to pro- 2 vide for building a wound core from sheet magnetic material with substantially only a single thickness of mica flakes between laminations so as to achieve a high space factor.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

For a better understanding of the nature and objects of the invention, reference should be had to the following detailed description and drawing, in which:

Figure 1 is a'schematic view of an apparatus- 25 tion obtained. A resistance of at least one ohm per square centimeter between each lamination is required as a minimum resistance for satisfactory low loss cores.

According to thepresent invention, sheet ferrous magnetic material of any kind is produced with an extremely thin layer of inorganic mica insulation on one surface and wound into a core having a high space factor. The wound core with applied inorganic mica insulation is heatjtreated 35 to remove all strains and to secure the best magnetic properties.

It has been discovered that if the surfaces of the strips of magnetic material are lightly coated w-th an easily volatilizable adhesive capable of adhering to the magnetic material and to mica flakes, a substantially single thickness of mica flakes may be applied thereto and held in place for a length of time to enable the making of a wound core therefrom. Readily volatile adhesives suitable for' the practice of the invention are glycerol, ethylene glycol, propylene glycol, castor 011, short chain liquid aliphatic hydrocarbon compounds, and gum elemi. The adhesive should substantially completely evaporate at to moderate temperatures, preferably below 300 C;

The adhesive may be applied by a roll coatin process or by spraying or equivalent method. Thin layers of adhesive just suflicient to retain the mica on the surface of the magnetic sheet material are preferred. An excess of the adhesive not only is uneconomical but may permit the mica flakes to accumulate several thicknesses deep. Further, excess adhesive may cause the mica flakes to slip and to squeeze out when a core is wound from the strip material.

Mica flakes for practicing' the inventio have been found to give the best coatings when divided to a size passing through a V inch mesh screen but held on a 100 mesh screen. Mica dust flner than 100 mesh is not particularly beneficial. Mica flakes of this size have necessarily been subjected to forces sufllcient to break up the flakes into the thinnest possible laminae, usually of a thickness of less than one mil. Furthermore, almost complete coverage of the surfaces of sheet materialhas been secured when the mica flakes are of the size indicated. Good results have been obtained Where the mica flakes have been as large as inch mesh. Likewise, mica flakes passing through a M; inch mesh screen and held on a 100 mesh screen have given good results. It Will be obvious that where ordinary magnetic iron sheet material is made into cores, low losses may not be critical and the mica employed may vary from these sizes, whereas for maximum efliciency ordinarily called'for when preferentially oriented material is employed, the selection of the size ",of mica flakes is critical.

Flaky materials suitable for the practice of the invention are various types of mica such as muscovite, phlogopite and vermiculite. Sheets or flakes prepared from bentonite, with or without inorganic additions, may be cut into flakes of a size usable for the invention. Also thin flakes of glass of suitably high melting temperature may be employed. Other flake-like substances ,may be obviously applied as described herein.

.- Referring to Fig. 1 of the drawing, there is illustrated an apparatus for practicing the invention. The roll In, of strip magnetic material mounted for free unwinding is composed of the continuous strip l2 of silicon iron or the like. The strip I2 is passed between the upper roll I and the coating roll l6 mounted within a receptacle i8 carrying an adhesive 20, such, for example, as glycerine. One side only of the strip need be coated. though for some purposes both sides may be coated if it is desired to apply mica insulation to both sides.

The adhesive coated strip I2 is conveyed through the enclosed casing 22 provided with a narrow aperture 24 accommodating the strip l2 and having suflicient clearance to prevent any adhesive being scraped off. Likewise, an exit aperture 26 closely accommodating the strip I2 is provided at the opposite end of the housing 22. The lowermost lower coated side of the strip i2 is subjected to a stream 21 of air-borne mica particles of the size-described herein. The airborne mica impinges against the adhesive and is retained if any portion of the surface of the adhesive coated surface of the strip is exposed. In this way, all exposed parts of the surface are com letely coated with the mica flakes while mica coated surfaces will not retain mica flakes blown thereagainst. Thereby substantially only a single layer of mica flakes is held by the adhesive. There may be a slight overlapping between the mica flakes; however,

this has been found to be negligible in increasing space factor. The stream of mica flakes is blown through the tube 28 by a stream of air delivered from a source such as a blower (not shown) to which mica flakes are fed continua y at a predetermined rate by the screw ill disposed in the housing 32 connected to the tube 28. A controllable speed motor it drives the screw 3|. A mica feed pipe 36 continually replenishes the screw 30 from the storage bin and collector unit 38. I

The housing 22 is provided with a hood 4! for exhaustin the excess mica flakes and the air introduced'through tube 28. It will be apparent that a great excess of mica flakes is introduced above that required to coat the bottom side of strip I 2. An exhaust fan 42 driven by motor H is connected by the tube 46 to the hood III for withdrawing the mica flakes and exhausting the mica flakes through the outlet 48 into the separator and collector 38. The separator 38 may be a conventional type of centrifugal separator capable of separating the mica flakes from the air and making them available for reuse.

The mica flake coated strip l2 now passes to a core winding machine under a guide roll 50. The core Winding machine may be composed of a rotating plate 52 carrying a mandrel 5| corresponding to the desired shape of window for the core. Obviously, the core may be of circular cross section or any other predetermined shape or size. The laminations are subjected to pressure from an oscillating head 56 provided with a pivotable arm 58 carrying two follow-up rollers 60 for applyin pressure to the sheet material in order to secure predetermined spec's factor. After a core of predetermined size has n wound, the sheet material may be cut and theloose end fastened to the body of the core by appropriate means, as by welding. The wound core may be subjected to a heat treatment which should be so conducted initially at a low temperature that the adhesive is caused to evaporate without forming any carbonaceous residue and leaving only the mica flakes between the laminations. Thereafter, the core may be subjected to higher temperatures of the order of 600 to 1000 C. to strain anneal the wound core and to accomplish any other purpose, including the completion of the process of orienting the crystals in the magnetic material.

The strip I2 is illustrated with greatly enlarged detail in Fig. 2 where the adhesive 82 and the substantially single thickness of mica flakes BI is evident. It will be appreciated that the total thickness of the layers 62 and Btis usually less than one mil. Cores wound from [5 mil sheet material have been regularly'made with space factors of and higher.

The invention has given excellent results in practice. In many cases, the losses in the core have been approximately those of the Epstein tests of the magnetic material.

The invention is not necessarily limited to the manufacture of wound magnetic cores but may be employed with success in making coils from copper sheet or strap. Since copper sheet or strap need not be strain annealed, a high temperature adhesive that need not be removed by evaporation may be fully adequate. For instance a thin layer of a liquid silicone resin may be employed as the adhesive for the mica flakes.

Although this invention has been described with reference to a particular embodiment thereof, it is of course, not to be liniited thereto except insofar as is necessitated by the scope of the appended claims.

We claim as our invention:

1. In the method of preparing annealed insul-ated cores of high space factor from sheet magnetic material the steps comprising, applying to the underside of strips of the magnetic material a thin coating of a readily volatilized adhesive composition composed of an organic liquid having a boiling point below 300 C. capa ble of adhering to the magnetic material and to thin flake-like insulation, thereafter applying an air-borne suspension of flake insulation of a size held on a 100 mesh screen and passing through a inch mesh screen to the coating of the adhesive composition whereby substantially a single thickness of flake insulation is adherently held by, the adhesive composition and any excess falls off, winding a core from the strip magnetic material carrying the flake insulation and heat-treating the wound core to drive off the adhesive composition and to anneal the sheet magnetic material to relieve strains developed during winding.

2. In the method of preparing annealed insulated cores of high space factor from sheet magnetic material the'steps comprising, applying to strips of the magnetic material a thin coating of a readily volatilizedadhesive composition composed of an organic liquid having a boiling point below 300 C. capable of adhering to the magnetic material and to mica flakes, blowing mica flakes of a size passing through /4 inch mesh but retained on a 100 mesh screen upwardly against the coating of the adhesive composition whereby substantially a single thickness of mica flakes is adherently held by the adhesive composition, any excess mica flakes dropping off, winding a core from the strip magnetic material carrying the mica flakes and heattreating the wound core to drive off the adhesive composition and to anneal the sheet magnetic material to relieve strains developed during winding.

3. The method of preparing annealed insulated wound cores of high space factor from sheet magnetic material comprising, applying to the underside -'of strips of the magnetic material a thin coating of a readily volatilized adhesive composition composed of an organic liquid having a boiling point below 300 C., applying an air-borne suspension of mica flakes of a size held on a 100 mesh screen and passing through a inch mesh screen to the coating of the adhesive composition whereby substantially a single thickness of mica flakes is adherently held by the adhesive composition and any excess falls off,

winding :3. core from the strip of magnetic material carrying .the mica flakes and heat-treating the wound core to drive on the adhesive composition and to anneal the magnetic material to relieve strains developed during winding.

4. In the method of preparing annealed insulated wound cores of high space factor from sheet magnetic material the steps comprising, applying to one side of strips of themagnetic material a. thin coating of a readily volatilized adhesive composition composed of an organic liquid having a boiling point below 300 C., blowing mica flakes of a size passing through A inch mesh but retained on a mesh screen upwardly against the coating of the adhesive composition whereby substantially a single thickness of mica flakes is'adherently held by the adhesive composition, any excess mica flakes dropping oif, winding a core from the strip of magnetic material carrying the mic-a flakes and heat treating the wound core to drive off the adhesive composition and to anneal the magnetic material to relieve strains developed during winding.

5. In the method of preparing an insulated wound member from metallic strip material, the steps comprising applying to one side of a metallic strip a thin coating of an adhesive composition, blowing small mica flakes passing through a V2 inch mesh screen but held on a 100 mesh screen upwardly against the coating of adhesive composition whereby substantially a single thickness of mica flakes is adherently held on the surface of the strip material by the adhesive composition and winding the metallic strip material carrying the mica flakes into a wound member with mica flakes between adjacent turns to provide a high space factor.

MORGAN W. RIDER. WELDON H. BRANDT.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Wintermute Sept. 12, 1939 

